The present invention relates to a magnetic recording/reproducing apparatus for a perpendicular magnetic recording medium and, more particularly, to a magnetic reproducing system.
With a conventional recording/reproducing system adapted for an in-plane oriented magnetic recording medium a ring-shaped magnetic head is used for recording and reproduction. To record a signal on the medium, a current is applied to the winding of the head so that a magnetic field generated across the head gap magnetizes the recording medium. To reproduce the signal from the recording medium, an electromotive force induced in the head in response to the signal magnetization on the medium is taken out as a reproduced signal. This system has a problem in that as the recording wavelength becomes shorter, the demagnetizing field effect increases. The system also has the defect that in reproducing, since the ring-shaped head is a magnetic flux detection type, the magnitude of the reproduced output signal depends upon the width of the track. Thus, the conventional system has a limitation on a high density recording and reproducing.
With a recently developed perpendicular magnetic recording/reproducing system a signal is recorded in a direction perpendicular to the plane of the recording medium. This system is not adversely affected by a demagnetizing field, and is essentially suitable for high density recording because the shorter a signal becomes in wavelength, the better recording is attained. However, with this conventional system reproduction is effected by detection of magnetic flux so that the magnitude of a reproduced output depends upon the width of a track. Therefore, taking into account the S/N ratio and reproducing sensitivity, the high-density recording cannot be effectively used.
A system for reproducing a signal by detecting a signal magnetic field from a magnetic recording medium is disclosed in Japanese Patent Early Publication No. 57-36407. This system uses as a magnetic head a magnetic material with an inductance element coupled thereto, the magnetic head being used as a constituent of a tuning circuit. In this system, a variation in magnetic field from the recording medium causes the permeability (.mu.) of the magnetic material of the head to vary, resulting in the shift of a tuning frequency of the tuning circuit, or the quality factor (Q) of the tuning circuit to vary. The variation in the tuning frequency and/or Q of the tuning circuit is used to take out the variation of the resonance output voltage of the tuning circuit. With this system, a slight variation in magnetic field from the recording medium results in a great variation in voltage. According to the reproducing system, therefore a reproduced output having high S/N ratio can be obtained even if the width of the recording track is narrow, thereby allowing high-density recording and reproducing.
A magnetic material having a high permeability causes in general a ferromagnetic resonance absorption phenomenon in a high frequency region. The permeability and loss of the magnetic material remarkably alter in the high frequency region even if the external magnetic field only slightly changes. Therefore, the above-mentioned reproducing system arranged to detect the signal magnetic field through the magnetic material is essentially suited for the high density recording/reproducing with narrow tracks because the reproduced output level depends only upon the intensity of the signal magnetic field rather than depending upon the magnetic flux. It is accordingly considered that an extremely high-density recording/reproducing system will be realized by combining this reproducing system with the perpendicular magnetic recording system.
However, this reproducing system has a problem in respect of the recording wavelength characteristics. This is due to the relationship between the distribution of the signal magnetic fields on the magnetic recording medium and the shape of the magnetic material. More specifically, the signal magnetic field on the magnetic recording medium becomes stronger as the wavelength is shorter, concentrating in the vicinity of the recording surface. The signal magnetic field becomes weak as the wavelength becomes long, spreading from the recording surface. Consequently, since the intensity and distribution of the magnetic field acting on the magnetic material are not uniform over the entire wavelength range, it is difficult to obtain a flat reproducing frequency response over a wide frequency range. The reproducing system is not practically suited for reproduction of video signals or audio signals.